May 4, 2001

The Strike Zone

Looking at Some Data

by Baseball Prospectus

With almost five weeks of baseball behind us, let's take a look at offense in the major leagues to see what, if any, impact the changes in the strike zone are having.

Ball Four and Strike Three

First, here's the basic walks and strikeouts information (through May 2), and the comparable information for April of 2000 (Ed. note: I apologize for the slight difference in endpoints.--JSS):

2001, American League

BB/9    K/9   K/BB
3.31   6.47   1.95

April 2000, American League

BB/9    K/9   K/BB
3.79   6.32   1.67

2001, National League

BB/9    K/9   K/BB
3.49   7.19   2.06

April 2000, National League

BB/9    K/9   K/BB
3.84   6.75   1.76

It's clear that the new strike zone is having an impact on these categories. Walks are down 12% in the AL and 10% in the NL. Strikeouts are up in both leagues, albeit by smaller margins, and the overall effect has brought the league K/BB ratios to right around 2-to-1.

Runs, and Other Fun Stuff

Have these changes reduced offense to date?

2001, American League

 AVG    OBP    SLG    R/9   HR/9
.260   .329   .417   4.78   1.09

April 2000, American League

 AVG    OBP    SLG    R/9   HR/9
.278   .351   .458   5.55   1.35

2001, National League

 AVG    OBP    SLG    R/9   HR/9
.259   .332   .433   4.88   1.30

April 2000, National League

 AVG    OBP    SLG    R/9   HR/9
.264   .345   .442   5.34   1.29

Wow.

All indicators of offense are down, led by on-base percentage. That's a natural indicator of a larger strike zone, as fewer walks are being drawn. Batting average is off in both leagues. Slugging average isn't down by nearly as much in the NL as it is in the AL, which may be an effect of the two new parks in the senior circuit.

Of course, run scoring is clearly down, by a whopping 14% in the AL and a mere 9% in the NL.

Home runs have been included because of a comment KZNE's Louie Belina made in an on-air conversation with Joe Sheehan on Thursday. While homers are down about 20% in the AL, they're not down at all in the NL, and overall, the dip that is less than that we've seen in overall offense.

That may be a Miller Park issue, but the data could also be interpreted as supporting a notion some people believe. Hitters more apt to swing at a high pitch may not increase their success overall, but the positive events--long hits--will compensate in part for lowered batting averages and OBPs.

Breaking it Down

How is the drop in offense happening? Well, pitchers are trading about 1.5% of their 1-0 counts for a comparable amount of 0-1 counts. That's less than a batter per game, and may not be significant for one month of play. However, there has been a big dropoff in performance following a 1-0 count. guys just aren't killing pitchers when they're ahead in the count they way they have in previous years.

American League
        2000            2001             Change
         %   OPS       %   OPS       %    OPS     Run
1st p  12.5  897     12.2  902     -0.3    +5    +1.1%
0-1    43.8  669     45.8  634     +2.0   -35   -10.5%
1-0    43.6  886     41.9  803     -1.7   -83   -18.7%

National League

1st p  13.1  909     13.3  888     +0.2   -21    -4.6%
0-1    43.5  642     45.8  636     +2.3   -6     -1.9%
1-0    43.4  861     40.8  848     -2.6   -13    -3.0%

The run column is the percent change in runs you'd expect from the changes in OPS. Last year, in both leagues, if the first pitch wasn't hit, it was about 50-50 as to whether it was a ball or a strike. This year, the strike is definitely favored.

If that pattern in ball/strike calling persists across all pitches, then there should be a larger increase in all "behind in count" amounts. That would mean hitters are hitting 1-2 more than 2-1, and so on. Over thousands of plate appearances, these small differences can have a big impact on the scoreboard.

Pitch Counts

With less offense and fewer walks, you might expect there to be an impact on pitches per game, and in the long run, pitcher workloads. Here's some information:

Average pitches per game per team 2001: 143.9
Average pitches per game per team 2000: 146.7
Average pitches per game per team 2000 through 4/30/2000: 148.0

Average pitches per inning 2000 through 4/30/2000: 16.6
Average pitches per inning 2000: 16.5
Average pitches per inning 2001: 16.1

There has been roughly a 3% drop in pitch counts so far compared to 2000. It's not clear that that's significant, given NP/IP in prior years:

Average pitches per inning 1999: 16.4
Average pitches per inning 1998: 16.1
Average pitches per inning 1997: 16.1
Average pitches per inning 1996: 16.2

What we're seeing is as likely to be regression to the mean as an actual effect from the changes to the strike zone.